Question

这是我的完整文档，我只需要它的子块＆＃39; One＆＃39;或者＆＃39;两个＆＃39;一次。

{
"_id": ObjectId('12abc'),
"createdAt": ISODate('2016-04-04T06:04:53.486Z'),
"updatedAt": ISODate('2016-04-04T06:04:53.486Z'),
"updatedBy": "SSE",
"DocName": "doc1",
"MainObj": {
    "One": {
        "color": {
            "green": [
                {
                    "val": "01",
                    "val2": "0"
                },
                {
                    "val": "10",
                    "val2": "5"
                }
            ],
            "result": "0000"
             }
         }

    "Two": {
        "color1": {
            "blue": [
                {
                    "val": "01",
                    "val2": "0"
                },
                {
                    "val": "10",
                    "val2": "5"
                }
            ],
            "result": "0000"
             }
                    }
               }
}

这是我预期的阻止：一个＆＃34;：{ ＆＃34; color＆＃34;：{ ＆＃34;绿色＆＃34;：[ { ＆＃34; val＆＃34;：＆＃34; 01＆＃34;，＆＃34; val2＆＃34;：＆＃34; 0＆＃34; }， { ＆＃34; val＆＃34;：＆＃34; 10＆＃34;，＆＃34; val2＆＃34;：＆＃34; 5＆＃34; } ] ＆＃34;结果＆＃34;：＆＃34; 0000＆＃34; } } }

Answer 1

您可以通过将子文档（MainObj.One）投影到名为One的变量中然后仅返回该变量来使用聚合框架执行此操作。例如：

db.YourCollectionName.aggregate([
    {$project:{One:"$MainObj.One"}},
    {$project:{_id:0,One:1}}
]);

返回：

{ "One" : { "color" : { "green" : [ { "val" : "01", "val2" : "0" }, { "val" : "10", "val2" : "5" } ], "result" : "0000" } } }

有关聚合框架和$project运算符的更多信息：

https://docs.mongodb.org/manual/reference/operator/aggregation/

更新：以下是包含createdAt，updatedAt，updatedBy和DocName的代码：

db.YourCollectionName.aggregate([
    {$project:{One:"$MainObj.One",createdAt:"$createdAt",updatedAt:"$updatedAt",updatedBy:"$updatedBy",DocName:"$DocName"}},
    {$project:{_id:0,One:1,createdAt:1,updatedAt:1,updatedBy:1,DocName:1}}
]);

返回：

{
    "createdAt" : ISODate("2016-04-04T06:04:53.486Z"),
    "updatedAt" : ISODate("2016-04-04T06:04:53.486Z"),
    "updatedBy" : "SSE",
    "DocName" : "doc1",
    "One" : {
        "color" : {
            "green" : [ { "val" : "01", "val2" : "0" }, { "val" : "10", "val2" : "5" } ],
            "result" : "0000" 
        }
    }
}

注意：更简单的方法如下：

db.YourCollectionName.find({},{createdAt:1,updatedAt:1,updatedBy:1,DocName:1,"MainObj.One":1});

唯一的区别是，这会将One作为MainObj的子文档返回（与原始问题中的内容不同）：

{
    "createdAt" : ISODate("2016-04-04T06:04:53.486Z"),
    "updatedAt" : ISODate("2016-04-04T06:04:53.486Z"),
    "updatedBy" : "SSE",
    "DocName" : "doc1",
    "MainObj" : {
        "One" : {
            "color" : {
                "green" : [ { "val" : "01", "val2" : "0" }, { "val" : "10", "val2" : "5" } ], 
                "result" : "0000"
             }
        }
    }
}

如何在mongoDB中获取嵌套元素？

1 个答案: